(1) Field of the Invention
The present invention relates to an apparatus for effectively removing harmful objects, which are included in a gas which is, for example, produced in a process of manufactuirng a semiconductor element.
(2) Prior Art
Recently, computers and electric control devices utilizing the computers have been progressed remarkably, and it seems that development of these industries expands widely and infinitely. Now, technique in manufacturing semiconductors, which lakes an important position as electronic parts used for a computer, and also the gross of its production are growing remarkably and rapidly.
Germanium (Ge) and silicon (Si) are normally used as raw materials for the semiconductor elements, and as a special semiconductor element, gallium-arsenic (GaAs) and gallium-phosphorus (GAP) and the like are utilized.
The processes for manufacturing semiconductor elements comprises, for example, a column forming process for forming a column of the semiconductor, a wafer forming process for slicing the column of the semiconductor, an element forming process for forming a number of elements by repeating the processes of masking the wafer, forming a thin film thereon, doping and etching the same, and a cutting process for cutting the treated wafer into each of the elements.
In the manufacturing processes, it is known that very fine particle dust such as 0.01-50 .mu.m is generated. It is also known that such fine particle dust is sometimes a harmful object which is prohibited to be abandoned in view of prevention of enviromental pollution, arid the gas itself including such a fine particle dust is a harmful object. Further, the fine particle dust sometimes absorbs or adsorbs a harmful object.
The harmful objects generated or used in the semiconductor manufacturing are such as silicon, arsenic, phosphorus, boron, metallic hydrogen, fluorine, halogen, halide, nitrogen oxides and the like, which will be referred to below.
As the silicon harmful gas, it may typically cite monosilane (SiH.sub.4), dichlorosilane (SiHCl.sub.2), silicon trichloride (SiHCl.sub.3), silicon tetrachloride (SiHCl.sub.4), silicon tetrafluoride (SiF.sub.4), disilane (Si.sub.2 H.sub.6), or TEOS(Si(OC.sub.2 H5).sub.4).
As the arsenic harmful gas, it may represent: arsine (AsH.sub.3) , arsenic fluoride (III)(AsF.sub.3), arsenic fluoride (V)(AsF.sub.5), arsenic chloride (III) (AsCl.sub.3), or arsenic chloride (V) (AsCl.sub.5).
As the phosphorus harmful gas, it may represent phosphine (PH.sub.3), phosphorus fluoride (III) (PF.sub.3), phosphorus fluoride (V) (PF.sub.5), phosphorus chloride (III) (PCl.sub.3), phosphorus chloride (V) (PCl.sub.5), or phosphorus oxychloride (POCl.sub.3).
As the boron harmful gas, it may cite diborane (B.sub.2 H.sub.6), boron trifluoride (BF.sub.3), boron trichloride (BCl.sub.3), or boron tribromide (BBr.sub.3).
As the metallic hydrogen harmful gas, it may list up hydrogen selenide (H.sub.2 Se), monogermane (GeH.sub.4), hydrogen telluride (H.sub.2 Te), stibine (SbH.sub.3), or hydrogen tin (SnH.sub.4).
As the fluorine harmful gas, it may, for example, cite methane tetrafluoride (CF.sub.4), methane trifluoride (CHF.sub.3), methane difluoride (CH.sub.2 F.sub.2), propane sixfluoride (C.sub.3 H.sub.2 F.sub.6), propane octafluoride (C.sub.3 F.sub.8).
As the harmful gas of halogen and halide, fluorine (F.sub.2), hydrogen fluoride (HF), chlorine (Cl.sub.2), hydrogen chloride (HCl), carbon tetrachloride (CCl.sub.4), hydrogen bromide (HB), nitrogen trifluoride (NF.sub.3), sulfur tetrafluoride (SF.sub.4), sulfur sixfluoride (SF.sub.6), tungsten sixfluoride (VI) (WF.sub.6), molybdenum sixfluoride (VI) (MoF.sub.6), germanium tetrachloride (GeCl.sub.4), tin tetrachloride (SnCl.sub.4)), antimony pentachloride (V) (SbCl.sub.5), tungsten sixchloride (VI) (WCl.sub.6) or molybdenum sixchloride (VI)(MoCl.sub.6).
As the harmful gas of nitrogen oxides, it may cite nitrogen monoxide (NO), nitrogen dioxide (NO.sub.2), or dinitrogon oxide (N.sub.2 O), and as the other harmful gas, it may also cite hydrogen sulfide (H.sub.2 S), ammonia (NH.sub.3), and trimethylamine (CH.sub.3).sub.3 N.
Further, it is known that fine particle dust may be produced in such a gas including ethane (C.sub.2 H.sub.5), propane (C.sub.3 H.sub.8), which have inflammability, and nitrogen (N.sub.2), oxygen (O.sub.2), argon (Ar), nitrogen dioxide (NO.sub.2) and the like.
Nowadays, the mind of preventing a public nuisance is thoroughly permeated. In such a state, it cannot accept to directly discharge the exhaust gas including the above harmful components or fine particle dust into the air, and it is required to give a suitable treatment to the exhaust gas so as to change the harmful gas to be a safe and clean gas. Therefore, as shown in FIG. 4, the exhaust gas is filtered out from an exhaust gas generator 1 by means of a pump 2 and fine particle dust of the exhaust gas is removed by a dust collector 3, and then a harmful component removing device 4 gives the gas a treatment of oxidation, reduction, adsorption or absorption.
As the dust collector, it may use a well known dust collector such as cyclone, a scrubber, a venturi scrubber, a bag filter, an electric collector, a looper and a settler. However, it is preferable to use an apparatus for treating a very fine particle dust, which is the prior invention (Japanese patent application No. 5-113927) of this applicant. This apparatus has high ability of collecting a dust and needs a small area of collecting.
The above apparatus for removing a harmful object uses, as shown in FIG. 5, a cylindrical casing 101 in which a harmful object treating material 102 is filled. The casing 101 has an inlet 103 at the lower end thereof and an outlet 104 at the upper end thereof, and also provides a supporting frame 105 which is fixed to the lower portion of the interior of the casing.
Further, the supporting frame 105 provides a supporting plate 106 which comprises a punched metal, and the supporting plate 106 supports the harmful treating material 102.
The harmful treating material 102 comprises, for example, a granular or lumpish base element having a diameter of 5-18 mm, and a harmful treating material. As the base element, it may cite, for example, active carbon, ceramics, plastics and the like, and as the harmful treating material, it may frequently use a platinum catalyst, an alkali metal silicate or a metal phosphate.
In the conventional apparatus for removing a harmful object, the exhaust gas including a harmful component easily flows in the area (the area shown with hatching of small pitch in FIG. 5), which flows to the outlet 104 straight from the inlet 103 of the casing 101, since a passage 108 may be formed in the area. However, since the passage 108 is narrow, its removing effect becomes low and the harmful treating material 102 around the passage 108 almost never functions and the ability of removing the harmful object becomes low in a short time. Thus, it has a disadvantage that the expected life span of the apparatus becomes short.
Further, in the conventional apparatus for removing the harmful object, it has been tried to control the exhaust gas to flow through the passage 108 with the function of atmospheric pressure by providing the inlet 103 at the lower end of the casing 101 and also the outlet 104 at the upper end thereof, so that the exhaust gas may sufficiently contact the harmful treating material 102 which is positioned outside the passage 108 in the casing 101. However, since the exhaust gas is urged by the pressure of the pump 2, such an idea almost never influences the efficiency of removing the harmful objects.
Furthermore, since the supporting plate 106 supporting the harmful treating material is constructed by a punched metal, the exhaust gas cannot flow at the portions of the harmful treating material which correspond to the portion of the supporting plate 106 where the punched openings are not located. Since the harmful treating material in the granular or lump form contacts the punched openings and closes same, the efficiency of utilizing the harmful treating material becomes low. Therefore, it is very disadvantageous in increasing not only the efficiency of using the harmful treating material, but also the expected life span of the apparatus.